Thats a link to a step down module my team is thinking of using to connect the VRM 12V ports to some arduinos. I read to rules and didn’t see anything against but I coulda missed something so hoping someone could confirm the legality.
Thanks!!

Yes, this item is legal for use on an FRC robot. In fact, a similar device was used to power radios in years past.
I would avoid connecting it to the VRM powering the radio though. The 12v rail only supplies a maximum of 2A peak and 1.5A continuous. The radio itself uses 1A which leaves you with only 500mA.
Just connect it directly to the PDP.

Another option would be to connect an additional VRM instead of buying this device. Most teams have an extra lying around.